BCM2712 IOMMU: Allocate tables on demand; make IOVA base address and size configurable #6997
Conversation
njhollinghurst
force-pushed
the
iommu-202508
branch
from
4db0efd to
2111273
Compare
njhollinghurst
changed the title
njhollinghurst
force-pushed
the
iommu-202508
branch
from
2111273 to
7de8409
Compare
|
Briefly tested with In this scenario, IOMMU allocated (16K) pages reached 93, so the change seems to be saving about 4.5 MBytes. More soak testing would be advisable. |
njhollinghurst
force-pushed
the
iommu-202508
branch
2 times, most recently
from
d638a92 to
5e8b30d
Compare
|
Although it's configurable, I have held off increasing the default aperture size (which remains 2GB per IOMMU) so we can be certain that worst-case memory usage can't increase. A bit more investigation may be needed to see if the DMA framework's allocator is willing to re-use virtual addresses (it appears so) rather than keep generating new ones; or if it would be beneficial to scavenge or free unused L2 pages (which might require keeping a use-count for each one and perhaps a free-list). But that's something for a future PR. |
Allocate space for level-2 IOMMU translation tables as needed. This should save memory in most cases but it means that map() can now fail with -ENOMEM. We don't currently free unused tables. Add OF properties to override the default aperture size (2GB) and base address (40GB; this doesn't include dma-iova-offset). Various tidy-ups. The internal representation of aperture limits does include dma_iova_offset, as that is more commonly useful. Clarify the distinction between Linux pages and IOMMU table pages. Fix wrong definition of MMMU_CTRL_PT_INVALID_EN flag. Signed-off-by: Nick Hollinghurst <[email protected]>
njhollinghurst
force-pushed
the
iommu-202508
branch
from
5e8b30d to
77be064
Compare
The first change is a draft of something we might actually want to do for Raspberry Pi 5.The second change is just for testing, to see if increasing IOVA can help resolve an issue with two 64Mpix cameras.
This has now been rebased and includes allocate-on-demand.